1. Field of Art
The disclosure generally relates to the field of battery cell assemblies.
2. Description of the Related Art
Recent advances in batteries based on lithium chemistries have led to the development of small batteries with extremely high energy density. Unfortunately the inherent thermal stability problems associated with lithium based chemistries severely limits the size of these batteries. The safest and most common lithium based battery is the lithium ion cell which are available in a small cylindrical form.
There are many devices, for example electric vehicles, that require large stores of energy for electrical power. To address these needs conventional approaches create a battery assembly out of many individual smaller cells and connect them in both series and parallel. This configuration typically produces a desired combination of output voltage and current. In many configurations using this conventional approach, hundreds of cells may need to be connected together in order to achieve the sought combination of output voltage and current. This task of assembling hundreds of cells together in a robust and economical way is a new challenge that is not adequately solved by conventional assembly methods.
Manufacturing battery cell assemblies requires significant care and precision in order to create a viable product. For example, with respect to these conventional assemblies, cells are electrically connected to each other by cell interconnects. These cell interconnects are typically made from thin strips of nickel or stainless steel. The cell interconnects are connected to each cell by either spot welding or soldering. The cell interconnects must be thin enough to weld to the cell without damaging the cell from excessive welding or soldering heat. In addition, most battery cells, particularly those based on lithium chemistry, are very intolerant of heating. Overheating these types of cells damages the cell chemistry. The result is reduced cell capacity to store energy or premature cell failure.
As for application of the battery cell assemblies, many devices such as electric vehicle applications require large amounts of peak current flowing through the assembly, oftentimes on the order of 300 amps. Thus, the cell interconnects must be large enough to carry this heavy current load. Unfortunately, these large interconnects are too large to weld or solder to the cells without damaging them. Moreover, a reliability problem arises when using large interconnects because they are too stiff. The stiff interconnects do not allow for cell movement that might occur during thermal expansion or vibration.
In an attempt to address these significant shortcomings, conventional approaches have incorporated a complicated solution that requires use of a two part cell interconnect. The first part of this two-part interconnect is a smaller interconnect that can be soldered or welded to the cell. Thereafter, the smaller interconnect is then soldered or welded to a second interconnect that is larger and heavier than the first interconnect. The added complexity of this two part interconnect is magnified as more and more cells are connected together, for example, 100 cells connected together. Further manufacturing costs are increased due to doubling of the number of solder or weld connections that must be made. Moreover, the added connections also double the number of potential failure points in a cell assembly.
Thus, there is lacking, inter alia, a battery cell assembly that allows for high current carrying capacity, robust construction with flexibility, cost effective manufacturing and a reduction in the number of failure points within the assembly.